Applied Surface Science 327 (2015) 504–516 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Improved microbial growth inhibition activity of bio-surfactant induced Ag–TiO 2 core shell nanoparticles D. Nithyadevi a , P. Suresh Kumar b , D. Mangalaraj a,∗ , N. Ponpandian a , C. Viswanathan a , P. Meena c a Department of Nanoscience and Technology, Bharathiar University, Coimbatore 641 046, India b Thin Film and Nanomaterials Laboratory, Department of Physics, Bharathiar University, Coimbatore 641 046, India c Department of Physics, PSGR Krishnammal college for women, Coimbatore 641 004, India a r t i c l e i n f o Article history: Received 4 October 2014 Received in revised form 26 November 2014 Accepted 26 November 2014 Available online 3 December 2014 Keywords: Composite materials Chemical synthesis Electron microscopy (HRTEM & FESEM) Surface properties a b s t r a c t Surfactant induced silver–titanium dioxide core shell nanoparticles within the size range of 10–50 nm were applied in the antibacterial agent to inhibit the growth of bacterial cells. The single crystalline sil- ver was located in the core part of the composite powder and the titanium dioxide components were uniformly distributed in the shell part. HRTEM and XRD results indicated that silver was completely covered by titanium dioxide and its crystal structure was not affected after being coated by titanium dioxide. The effect of silver–titanium dioxide nanoparticles in the inhibition of bacterial cell growth was studied by means of disk diffusion method. The inhibition zone results reveal that sodium alginate induced silver–titanium dioxide nanoparticles exhibit 100% more antibacterial activity than that with cetyltrimethylbromide or without surfactant. UV–vis spectroscopic analysis showed a large concentra- tion of silver was rapidly released into phosphate buffer solution (PBS) within a period of 1 day, with a much smaller concentration being released after this 1-day period. It was concluded that sodium alginate induced silver–titanium dioxide core shell nanoparticles could enhance long term cell growth inhibition in comparison with cetyltrimethylbromide or without surfactant. The surfactant mediated core shell nanoparticles have comparatively rapid, less expensive and wider applications in modern antibacterial therapy. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In recent years; metal–oxide coated metal nanoparticles have attracted increasing attention due to their unique material char- acteristics such as thermal stability; electrical; catalytic; optical and biological properties [1,2]. They are generally called core/shell nanoparticles and combine the advantages of core metal particles and shell metal–oxide nanoparticles. There is a considerable inter- est in the development of synthetic protocols in order to control the size; shape; morphology and crystallinity of nanoparticles as their chemical and physical properties can differ vastly at the nanoscale compared to bulk materials; and with these new properties; they offer unique technological applications [3–5]. The surface function- alization of nanoparticles plays a fundamental role in their stability Abbreviations: TiO2, titanium dioxide; Ag, silver; CTAB, cetyltrimethylbromide. ∗ Corresponding author. Tel.: +91 422 2428421. E-mail addresses: dmraj800@yahoo.com, mangalaraj@buc.edu.in (D. Mangalaraj). and dispersion in diverse solvents. In general; the modification of the surface of nanoparticles with capping molecules contain- ing different types of functional groups is a good way of tuning their properties; turning nanoparticles into very useful nanostruc- tures; which can be applied in many fields. Titania [6]; cadmium sulphide [7]; zinc sulfide [8]; silica [9]; silver [10]; alumina [11] and zirconia [12] have been employed as materials for core and shells. Along with the core matrix; polymeric beads and polymeric col- loids containing functional groups have been mostly employed as capping molecules for cores. Uniform and controllable sizes; larger surface areas; adsorption capacities and easy preparation meth- ods make polymeric colloids as an attractive surfactant material in the preparation of metal/metal–oxide core shell nanoparticles. Furthermore, colloidal polymer coated core/shell particles can also be used in the production of inorganic hollow particles through removal of surfactants. Titania has received considerable attention as a material due to its scientific and technological importance over the last few decades [13–15]. Titania and titania-containing materials have been used as photocatalysts [10,16–20], catalyst supports [13–15,21–23], http://dx.doi.org/10.1016/j.apsusc.2014.11.169 0169-4332/© 2014 Elsevier B.V. All rights reserved.